A fluororesin has excellent properties such as heat resistance, weather resistance, chemical resistance, peeling properties, and low dielectric properties. The fluororesin is not only formed into a molded body but is also used as a coating material. Thus, layer with different materials has been investigated. However, the surface energy of the fluororesin is small, and the bonding of the fluororesin and different materials is difficult.
An investigation on the stacking of a composite structure in which an organopolysiloxane cured layer is formed on the surface of a fluorine-based polymer by introducing a silane gas into a vacuum plasma generator and performing vacuum plasma treatment on the fluorine-based polymer, and different materials is conducted (for example, refer to Patent Document 1). However, in order to obtain satisfactory bonding of the composite structure and different materials, a primer is required.
On the other hand, in the above-described method, an object to be treated having a size that can be accommodated in the plasma generator is treated batchwise. In contrast, a method of continuously performing plasma treatment on a long molded product has been investigated. For example, an alkoxysilane compound is applied to the inner surface of a plastic tube and the inner surface is subjected to plasma treatment by atmospheric pressure glow discharge in helium or a mixed gas atmosphere of helium and argon to form a thin film of silica. A plastic tube in which additives are not eluted from the inner surface of the tube has been investigated but the effect of bonding has not been investigated. Thus, it is considered that sufficient adhesiveness cannot be obtained in this method (for example, refer to Patent Document 2).